1. Field of the Invention
The present invention relates to a technology for controlling driving of transport rollers in a paper transport device for use in a paper processing apparatus.
2. Description of the Related Art
In a paper post-processing apparatus used with an image forming apparatus, when abnormal events such as paper-jamming, cover's opening during paper transport, or mechanical abnormality occur, paper cannot be transported in a desired manner. Therefore, when such events occur, entire driving of the paper post-processing apparatus is forced to stop. When a paper that has being transported is remained in the paper post-processing apparatus at the time of stopping of the driving, a paper removal process is firstly performed and then a recovery process is performed on a remained paper so that the remained paper is subjected again to image forming processing, post-paper processing, and paper ejecting processing.
However, when the leading edge of a paper is present downstream of a paper ejecting roller at the time of stopping of the paper post-processing apparatus, the paper may be ejected outside of the apparatus due to delay in stopping of the paper ejecting roller even when the apparatus commands to keep the paper inside of the apparatus. Alternatively, a user may pull out the paper when the leading edge of the paper is ejected outside of the paper post-processing apparatus, and may consider the paper as acceptable. In this case, because the paper-post processing apparatus considers that the paper is still remained in the apparatus although the paper is actually ejected, the recovery process including image forming processing and paper processing is re-performed, resulting in redundant output.
For example, Japanese Patent Application Laid-open No. H09-71363 discloses a sheet post-processing apparatus that can cope with the above situation. Specifically, the sheet post-processing apparatus includes a plurality of sheet processing units each of which can be driven independently to execute a sequential process along a flow of transporting a sheet. With this configuration, it is possible to eliminate a remained sheet removal process resulting from stopping of the apparatus and to prevent interruption of sheet processing. More specifically, the sheet post-processing apparatus includes a stopping unit that, when abnormality is detected in any one of the sheet processing units, stops the sheet processing unit with the abnormality; a selecting unit that selects another sheet processing unit to be stopped simultaneously with the sheet processing unit with the abnormality based on a position of the sheet processing unit with the abnormality; and a simultaneous stopping unit that stops the selected sheet processing unit.
Furthermore, another sheet post-processing apparatus is disclosed in Japanese Patent Application Laid-open No. H08-231121. The sheet post-processing apparatus is configured such that even if paper-jamming occurs in a post-processing apparatus, sheet (paper) transport in an image forming apparatus need not be stopped immediately and a sheet removal process can be carried out easily. Specifically, the sheet post-processing apparatus receives a paper ejected out from a paper ejecting unit of an image forming apparatus and transports the received paper through a single transport path to a sorting unit, where the paper is sorted out and is transported for sheet alignment. This sheet post-processing apparatus includes an entrance guide plate disposed at an entrance end of the single transport path facing the paper ejecting unit of the image forming apparatus, and a releasing unit that releases the entrance guide plate when paper-jamming occurs in the sheet post-processing apparatus.
However, if a paper at the upstream side is stopped while a paper at the downstream side is being transported, such a trouble as folding, tearing, and roller abrasion (soil) of the paper at the downstream side may occur on the paper at the downstream side, especially when the distance between both papers is short. For example, when the trailing edge of the downstream paper has not passed a stopped roller after an upstream processing unit is stopped or when the downstream paper comes in contact with the upstream paper and causes a paper-jamming, the downstream paper is damaged by folding, breaking, roller abrasion (soil), or the like.